Customizers should follow the example of Montgomery Scott:
Scotty Principle
(n.) The defacto gold star standard for delivering products and/or services within a projected timeframe. Derived from the original Star Trek series wherein Lt. Cmdr. Montgomery 'Scotty' Scott consistently made the seemingly impossible happen just in time to save the crew of the Enterprise from disaster.
The premise is simple:
1) Caluculate average required time for completion of given task.
2) Depending on importance of task, add 25-50% additional time to original estimate.
3) Report and commit to inflated time estimate with superiors, clients, etc.
4) Under optimal conditions the task is completed closer to the original time estimate vs. the inflated delivery time expected by those waiting.
Although maybe doubling the time estimate would be safer
5) Give her all she's got!